The present invention relates generally to laser systems and, more particularly, to a system and method for surface particle and thin film ablation.
In the production of integrated circuits, for instance, an image of a photo-mask is first projected onto a photoresist material or layer coated on a silicon wafer or the like. This is commonly known as the exposure step. The photo-mask contains pattern information corresponding to the structures required for the circuit to operate. A result of this step is selective modification of the resist layer into a pattern that corresponds to the master pattern on the photo-mask. Subsequent process steps are then used to selectively modify the wafer as well as generate a circuit layer corresponding an the mask image impressed upon the resist. By repeating this process on the wafer using a series of masks, an integrated circuit is constructed.
With the ever increasing miniaturization of integrated circuitry and, in particular, reduction in size of photo-mask features, there is a continuing need for further refinement of photolithographic processing. To this end, it is desirable to expand the capabilities of traditional microscope components not only for enhanced viewing, but also analysis and correction of defects on photolithographic masks.
Conventional photo-mask patterns are generated by laser or electron beam direct writing. In particular, a blank mask coated with a resist material is scanned by a laser or electron beam. The beam is modulated, on or off, to expose or not expose, respectively, the material at each point in the scan raster. When scanning or writing has been completed, the material is developed. Stated differently, where ever beam exposed resist material is present, it is removed by chemical action. This leaves behind an image in the resist of the pattern desired to be transferred onto the photo-mask. The photo-mask is then etched using either a wet process, an acid bath or dry etching by RF excited plasma. Once etching has been completed, where ever resist material has been removed, chrome is also removed. Finally, the excess resist material is stripped away thereby producing, for instance, a xe2x80x9cchrome on glassxe2x80x9d photo-mask ready for inspection.
While this process has been found useful, image defects are often formed during photo-mask production. These defects are generally known as (i) misplaced pattern defects, (ii) missing pattern defects, and (iii) foreign material or contamination defects.
Generally speaking, misplaced pattern defects are spots of material, e.g., native material, that the patterning process was unsuccessful in removing from the substrate. These defects are classified and named according to their effect on the mask pattern, i.e., as isolated spots, edge extensions and bridge defects.
Missing pattern defects, in turn, typically manifest as spots where native material has been removed unintentionally from the substrate. These defects are classified according to their appearance, namely, as pinholes, edge intrusions and broken line defects.
As for contamination defects or FM, they are classified as any material-type contamination found on the mask surface. While rigorous cleaning and handling procedures may be applied, FM defects usually remain. Moreover, the cleaning processes eventually become victims of diminishing returns, that is, additional cleaning cycles of a photo-mask used to remove one FM defect will often add new ones.
In general, there is an inverse relationship between defect density and defect size, namely, as defect density increases, the size of the defect decreases. Although relatively smaller sized defects have been considered acceptable by some, with the ever increasing demand for smaller and faster devices, there is a corresponding decreasing tolerance for the minutest of defects.
An apparatus and localized laser method is therefore desired for viewing, analyzing and eliminating relatively small defects on photolithographic masks including, but not limited to, misplaced pattern, and foreign material defects.
In accordance with one aspect of the present invention is a system for photolithographic mask repair, which comprises:
a structure for supporting a mask to be operated on;
a laser emitting device for effecting mask repair;
a light source adjacent to the support structure for selected illumination of the mask;
a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device, the processor including an adjustable beam splitter for effecting off-axis laser illumination, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
a computer device for controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
a microscope for multi-aspect viewing of the mask during navigation of the beam about the mask.
According to another aspect of the present invention is a system for photolithographic mask repair which comprises:
a structure for supporting a mask to be operated on;
a laser emitting device for effecting mask repair;
a light source adjacent to the support structure for selected illumination of the mask;
a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device, the processor including an adjustable beam splitter for effecting off-axis laser illumination, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
a computer device for controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
a microscope for multi-aspect viewing of the mask during navigation of the beam about the mask, the computer device, simultaneously with manipulation of the beam, effecting fine motion control of the beam, controlled movement of a motorized aperture for effecting the sequential angular manipulation, controlled support structure movement, and image data processing.
In accordance with a further aspect of the present invention is a system for photolithographic mask repair which comprises:
a structure for supporting a mask to be operated on;
a laser emitting device for effecting mask repair;
a light source adjacent to the support structure for selected illumination of the mask;
a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device;
a computer device for controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
a microscope for multi-aspect viewing of the mask during navigation of the beam about the mask, the microscope including a relatively low magnification video camera, a relatively high magnification video camera, and a DUV imaging and transmission measurement system.
According to yet another aspect of the present invention is a system for photolithographic mask repair which comprises:
a structure for supporting a mask to be operated on;
a laser emitting device for effecting mask repair;
a light source adjacent to the support structure for selected illumination of the mask;
a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device;
a computer device for controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
a microscope for multi-aspect viewing of the mask during navigation of the beam about the mask.
According to still another aspect of the present invention is a system for photolithographic mask repair which comprises:
a mask to be operated on;
a laser emitting device;
a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device, the processor including an adjustable beam splitter for effecting off-axis laser illumination, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
a computer device for controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
a microscope for multi-aspect viewing of the mask during navigation of the beam about the mask.
According to yet a further aspect of the present invention is a system for photolithographic mask repair which comprises a mask to be operated on, a laser emitting device, and a laser processor for effecting sequential angular manipulation of a laser beam projecting from the laser emitting device, the processor including an adjustable beam splitter for effecting off-axis laser illumination, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair.
Another embodiment of the present invention relates to a method for photolithographic mask repair comprising the steps of:
i. locating a photo-mask on a relatively stationary, isolated support structure;
ii. activating a laser emitting device for effecting mask repair;
iii. actuating a light source adjacent to the support structure for selected illumination of the mask;
iv. passing a laser beam emitted from the laser emitting device through a laser processor for effecting sequential angular manipulation of the laser beam, the processor including an adjustable beam splitter for effecting off-axis illumination of the laser beam, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
v. controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate uniform surface exposure in the target area; and
vi. simultaneously with the sequential angular manipulation, providing multi-aspect viewing of the mask during navigation of the beam about the mask, effecting fine motion control of the beam, controlled movement of the motorized aperture for effecting the sequential angular manipulation, controlled support structure movement, and image data processing.
A further embodiment according to the present invention is a method for photolithographic mask repair comprising the steps of:
i. activating a laser emitting device for effecting mask repair;
ii. locating a photo-mask on a relatively stationary, isolated support structure;
iii. actuating a light source adjacent to the support structure for selected illumination of the mask;
iv. passing a laser beam emitted from the laser emitting device through a laser processor for effecting sequential angular manipulation of the laser beam, the processor including an adjustable beam splitter for effecting off-axis illumination of the laser beam, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
v. controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate a more uniform surface exposure in the target area; and
vi. simultaneously with the sequential angular manipulation, providing multi-aspect viewing of the mask during navigation of the beam about the mask, effecting fine motion control of the beam, controlled movement of the motorized aperture for effecting the sequential angular manipulation, controlled support structure movement, and image data processing.
Still another embodiment of the present invention relates to a method for photolithographic mask repair comprising the steps of:
i. activating a laser emitting device for effecting mask repair;
ii. actuating a light source adjacent to the support structure for selected illumination of the mask;
iii. locating a photo-mask on a relatively stationary, isolated support structure;
iv. passing a laser beam emitted from the laser emitting device through a laser processor for effecting sequential angular manipulation of the laser beam, the processor including an adjustable beam splitter for effecting off-axis illumination of the laser beam, a motorized aperture for facilitating incremental mask repair, an optical system for image reduction, and a device for viewing the mask during repair;
v. controlling the sequential angular manipulation so as to capture a generally complete waveform of the beam and generate a more uniform surface exposure in the target area; and
vi. simultaneously with the sequential angular manipulation, providing multi-aspect viewing of the mask during navigation of the beam about the mask, effecting fine motion control of the beam, controlled movement of the motorized aperture for effecting the sequential angular manipulation, controlled support structure movement, and image data processing.
Accordingly, it is an object of the present invention to provide an improved system and method for photolithographic mask repair.
Another object of the present invention is to provide improved precision in photolithographic mask repair.
A further object of the present invention is to enhance resolution of a laser beam used for photolithographic mask repair.
Yet another object of the present invention is to provide a system for viewing, analyzing and eliminating surface defects from photolithographic masks.
Still another object of the present invention is to provide a system for real time viewing of a photolithographic mask during mask repair.
Yet a further object of the present invention is to provide a system for multi-aspect viewing of and navigation about a photolithographic mask.
A further object of the present invention is to provide a method for loading photo-masks of varying thicknesses while preserving top reference.
Still another object of the present invention is to provide illumination suitable for concurrently viewing patterns on, and laser repair of, photolithographic masks.
Another object of the present invention is to provide a system for improving and controlling images of photolithographic masks presented to a user by varying image magnification, illumination wavelength, illumination angle and/or polarization.
Yet another object of the present invention is to improve defect viewing of photolithographic masks using off-axis laser illumination.
Still a further object of the present invention is to provide repeatable control of the photolithographic mask, defect repair process using machine vision.
A further object of the present invention is to provide a system for photolithographic mask repair with an actuating focusing mechanism without backlash and auto-focusing.
Another object of the present invention is to improve selectivity of a laser machining process to preferentially remove opaque films from glass substrates, and foreign material from photo-masks.
Yet a further object of the present invention is to provide for the elimination of opaque defects and foreign material on peliclized photo-masks, and the deposition of removed material in the neighborhood of photo-mask repair.
The present invention will now be further described by reference to the following drawings which are not intended to limit the accompanying claims.